This invention is concerned with an apparatus for effecting compression, decompression and editing of signals, and it particularly relates to an apparatus for printing and displaying images.
In laser beam printers, for example, the transfer of recording paper and the printing operation are executed at the same speed. Since data is output so as to match the picture signal sent from a host computer with the printing speed of a printing device, a memory for storing image data of at least one image is generally required. However, a memory having a huge capacity becomes necessary in order to realize a high picture quality with high resolution and high gradation, color, etc.
An example of a printing apparatus having a reduced memory capacity in order to eliminate the above problem is disclosed in a preprint of xe2x80x9cImage compression encoding method optimized for a full-color printerxe2x80x9d, Japan Hardcopy ""94 Fall Meeting, The 74th Conference of Japan Hardcopy for the Society of Electrophotography of Japan, Nobutaka Miyake, p. 13-16 (Dec. 2, 1994). According to this paper, the memory capacity for storing image data is reduced by using image compression encoding means combining discrete cosine transformation and quantization.
Further, as means for signal compression at a fixed compression rate, the LSI under the product name of FBTC (IMAGE DATA COMPRESSION and DECOMPRESSION LSI), having the type name of M65790FP, is described in the Mitsubishi Electric Corporation""s data sheet. This LSI realizes a constant compression rate of 8/3 for black and white images so that the memory address at the time of the output of the compression data is converted to realize a processing of rotation and synthesis.
However, there are the following problems in the apparatuses disclosed in the above-mentioned publications:
(1) Regarding the apparatus in which image data is processed by using a compression method combining the discrete cosine transformation and quantization, the quantity of compressed data, that is, the compression rate changes in accordance with the patterns of the images. Therefore, the memory capacity must be designed, considering the worst compression rate.
(2) It is necessary to store image data of at least one page and rewrite the stored data so as to input page description languages, such as Post Script, as a command from the external apparatus, and to form and edit the image data. Since the compression rate changes in accordance with the pattern of the images, there is no regularity to the memory addresses at which the compression data is stored. Therefore, even if the image data to be rewritten is part of the image plane, all image planes must be decoded. Further, when the data of a part of the image is rewritten, the compression rate of the part changes and writing into the memory area can not be done.
(3) The picture quality degradation easily occurs due to compression processing of the image data. The Mitsubishi LSI has only the function of compressing and decompressing image data of every one image unit. And this device does not consider the editing function in order to rewrite the compression data stored. In addition, since the object of the Mitsubishi LSI is to produce a black and white image, signal processing for each color either must be executed in a time series, or several LSIs are necessary in order to carry out signal processing for the color image.
It is an object of the present invention to provide signal processing equipment which can reduce the memory capacity to be stored for forming or editing image data, solving the problems of the prior art.
A first feature of the present invention, in order to achieve the above object, is in the provision of signal processing equipment having compression means for converting signals into compression data on the basis of a compression procedure; storing means for storing the compression data; decompression means for restoring the compression data from the storing means in accordance with a decompression processing; and editing means for executing signal processing of the decompression signals; wherein the signals as the edit object are restored by using the decompression means from the storing means, and the processing result by the edit means is stored in the storing means by using the compression means.
Further, a second feature of the invention is in the provision of signal processing equipment having compression means for converting signals into compression data on the basis of a compression procedure; storing means for storing the compression data; decompression means for restoring the compression data from the storing means on the basis of a decompression procedure; and edit means for executing processing of the signals as the object stored in the storing means; wherein the signals to be the edited object are read out from the storing means, and the processing result by the edit means is stored in the storing means.
In addition, a third feature of the invention is in the provision of signal processing equipment having compression means for converting signals into compression data in accordance with a compression procedure; storing means for storing the compression data; decompression means for restoring the compression data from the storing means in accordance with a decompression procedure; edit means for executing signal processing of the decompressed signals; and a switch for changing the destination of the output of the signals restored by the decompression means; wherein the switch changes the destination of the outputs by the editing or the output of the signals.
The capacity of the memory for storing the image data is reduced, and, at the same time, the data transfer rate between the elements is reduced so that the formation and editing of the image data can be executed at a high speed, and so advantages not available in the conventional signal processing equipment can be obtained.